1. Field of the Invention
The present invention relates to artificial lift production systems and methods deployed in subterranean oil and gas wells, and more particularly relates to artificial lift production systems and methods having submersible transducers allowing two fluids to be produced separately.
2. Description of the Related Art
An oil producing reservoir or zone in a well has a natural pressure. A well that produces oil or gas by its own pressure is a flowing well. Stated another way, a flowing well is a well that is not being produced by the employment of transducers, such as pumps, or other artificial means. The natural pressure may not be sufficient to force the production fluid to the surface during the later or even from the beginning stages of the life of the well. In such instances, secondary methods of extracting the production fluid to the surface may be required to supplement the reservoir drive.
One type of secondary method of extracting the production fluid is through the use of an electric submersible pump, commonly referred to as an ESP. The ESP is lowered into the well and an electrical cable extends from the wellhead to the ESP. The ESP pumps the production fluid to the surface and aids in maximizing production from a low pressure or non-flowing well.
In many instances, two or more separate producing zones exist in a single well bore. In many of these multiple zone wells, it is desirable to produce the production fluids P1 and P2 from zones Z1 and Z2, respectively, concurrently and without commingling. For example, P1 and P2 may be at different reservoir pressures. If P2 has a higher pressure than P1 and they are produced commingled, the flow rate of the lower pressure reservoir P1 will be reduced because of the higher pressure of the other reservoir P2. Another example would be where one formation includes a corrosive gas or a damaging fluid that should not be commingled with the other formation. The two production fluids may not be compatible with each other. Yet another reason for producing without commingling is that certain regulatory agencies consider separated zones to be different fields and the operator has to report the flow rates from each individual reservoir. If the production fluids P1 and P2 are commingled downhole the operator has no way of accurately reporting the separate flow rates.
One option for producing two zones from a single well is for the operator to complete one zone for several years and then complete the second zone when the first zone is abandoned. Alternatively, the operator could drill a separate well for the second zone as opposed to waiting for several years and taking the risk that the economic value of the well may be significantly lower at that point in time. Thus, it is desirable to produce concurrently without commingling from two zones within a single well bore. It is even more desirable to be able to use an artificial lift system to separately produce fluids from multiple zones within a single well bore.
In an artificial lift system having a transducer, such as a submersible pump, the work required in the transducer is a finction of the volume being pumped. If the produced fluid includes both liquid and gas, the current state of the art places a liquid/gas separator on the transducer to remove the gas and reduce the fluid volume to be pumped by the transducer. The use of the separator to remove the gas allows the transducer to work more efficiently. However, it is to be understood that once that transducer fails it can only be replaced by pulling the combined transducer and separator assembly out of the well. Similarly, if the liquid/gas separator fails, the separator can only be replaced by pulling the combined transducer and separator assembly out of the well. Moreover, in many reservoirs where large amounts of gas are found with the associated liquids, the current state of the art requires the use of natural gas separation, and then placing the transducer below the resulting fluid level. Thus, it is also desirable to be able to use an artificial lift system to produce a gas and liquid production fluid from a single zone separately as a gas and a degassed fluid.
Various prior art patents disclose arrangements for producing from two separate zones in a single well. These patents include U.S. Pat. Nos. 3,115,185; 3,080,922; 2,905,099; 2,811,924; 2,799,226; 2,678,605; 2,642,803; and 2,242,166.
U.S. Pat. No. 3,115,185 discloses a dual completion apparatus having a pair of non-concentric tubing strings from the surface to a cylindrical upper body. The upper body has bores adapted to detachably receive the lower end of tubing strings. An outer pipe is attached to the lower end of the upper body, The lower portion of the outer pipe is sealingly engaged with an upper packer. An inner pipe is connected to the lower end of the bore in the upper body and extends through and below the outer pipe. The lower portion of the inner pipe is sealingly engaged with a lower packer. The lower packer is positioned above a lower zone and the upper packer is positioned above an upper zone. Production from the lower zone is produced through inner pipe and tubing string and production from the upper zone is produced through the annulus in outer pipe and tubing string.
U.S. Pat. No. 3,080,922 discloses a multiple zone well production apparatus having non-concentric dual tubing strings from the surface to a main head. The main head includes passages which are in fluid communication with the tubing strings. A lower string of tubing extends from the main head and through a lower packer for producing fluid from a lower zone below the packer. While not shown, it is suggested that suitable pumping equipment can be used in each tubing string to elevate the production to the top of the hole.
U.S. Pat. No. 2,905,099 discloses an oil well pumping apparatus for separately producing oil and gas from a lower producing zone in a dual zone well through concentric tubing.
U.S. Pat. No. 2,811,924 discloses an apparatus for separately and concurrently producing both oil and gas from two separate zones. A packer separates the two zones. Gas from the upper zone is produced through an upper pipe and oil from the upper zone is pumped by pumping jack through the production tubing. Gas from the lower zone is produced through an annulus between packer tubing and lower production tubing before entering the two-way crossover which diverts the gas to production tubing. Oil from the lower zone is pumped through the lower production tubing before entering the two-way crossover which diverts oil to production tubing.
U.S. Pat. No. 2,799,226 discloses a hydraulic pump assembly inserted in a tubing string. The pump assembly is adapted to remove fluid simultaneously from two separate zones without admixing the streams. Additionally, the pump assembly can be removed from the well without removing the entire well tubing.
U.S. Pat. No. 2,678,605 discloses a gas lift apparatus for producing oil from a multiple zone well. The oil is produced from separate zones through concentric tubing strings without admixing the streams. Gas lift valves are used to inject gas from the surface into the flowing oil stream to provide lifting action.
U.S. Pat. No. 2,642,803 discloses a dual production zone pump capable of pumping fluids simultaneously from spaced, subsurface formations while maintaining the pumped fluids segregated from each other.
U.S. Pat. No. 2,242,166 discloses an apparatus for employing two electric submersible pumps simultaneously in the same well for removing oil from two separate producing zones.
It is desirable to have an artificial lift system that allows for the concurrent and non-commingled production from more than one zone in the well bore of different pressures, fluids, gases, or solids using transducers, including transducers requiring an electrical power cable. It is also desirable that the artificial lift system include two electric submersible pumps with separate cables which are protected against damage during both installation and operation in the well. It is desirable that the electric submersible pumps be retrievable without having to retrieve the packer from the well bore. Additionally, it is important that the artificial lift system be capable of installation with a minimum of difficulty and risk of damage to the system as it is being installed. It is also desirable to have an artificial lift system that allows for the downhole separation of gas and degassed fluid and the separate production of each from a single zone.